It is often desired to produce a conformal polymer coating on selected areas of a substrate. Conventional methods for producing such a coating generally involve solution processing to achieve a substantially uniform layer of polymer over the entire substrate surface, followed by removing selected areas by photolithography. However, uniform coating followed by photolithography is not a suitable process for selective deposition of many polymers, since it involves use of solvents, acids, and water, all of which can lead to undesirable side reactions with the deposited polymer.
Prominent among the polymers for which photolithography processes are undesirable are electroluminescent (EL) polymers. These materials are promising for use as the active element in light emitting diodes (LEDs) and lasers, since polymers have advantages in processing and formation of strong, flexible, light weight structures. Some of the most attractive candidates for polymer-based LEDs are those derived from poly(p-phenylene vinylene) (PPV). Continuous thin films of PPV can be fabricated by solution processing methods, or by chemical vapor deposition. However, production of devices more complicated than a single monolithic LED requires subsequent photolithography, which can irreparably damage the unique electronic properties of these films. In particular, the incorporation of oxygen into the structure of PPV has been shown to be detrimental to the conductivity and to the photoluminescent (PL) and EL efficiencies of the film, through the formation of carbonyl defects.
It is thus desirable to produce patterned layers of polymer coatings directly, in which the polymer is selectively deposited only on the areas in which it is ultimately desired. For inorganic materials, it has been found that such selective deposition can be accomplished by a surface treatment of a substrate followed by chemical vapor deposition. The surface treatment is adapted to inhibit nucleation in some areas of the substrate, and/or to promote nucleation in other areas. By carefully controlling the processing conditions of the chemical vapor deposition, the inorganic material can be induced to deposit only on the favorable nucleation areas, producing a patterned layer of material.
A similar process is described in U.S. Pat. No. 5,618,379, in which exposure of selected areas of a substrate to a plasma inhibits the subsequent deposition of p-xylylene monomers to produce poly-p-xylylene in those areas. However, the use of a plasma is cumbersome and not suitable for all substrates, and no methods are disclosed for deposition of polymers other than poly-p-xylylene. In particular, no techniques are known for the selective deposition of PPV and its related compounds without subsequent solution processing.